A critical missing element in the rapid development of the field of optoelectric communications systems is the existence of means for direct electrical control of the optical mode propagating in a slab wave-guide in which the entire structure, both wave-guide and control means, are monolithically created from silicon by using techniques that are fully compatible with current very large scale integrated (VLSI) technologies.
The basic effect needed to supply such a solution is known and is based on the influence of the refractive index of a medium on the wave properties of an electromagnetic wave propagating in the medium. The effect of the free, carriers on the index of refraction in silicon, in a metal oxide semiconductor (MOS) structure has; been demonstrated via the electro-reflectance effect [J. A. Batista, A. M. Mansanares, E. C. da Silva, “Photothermal and Electroreflectance images of biased metal-oxide-semiconductor field-effect transistors: Six different kinds of subsurface microscopy”, J. Appl. Phys., 82 (1), pp 423–426 July (1997)]. Also a Mach-Zehnder modulator based on injection of free carriers has been shown [G. V. Treyz, P. G. May, Jean-Marc Halbout, “Silicon Mach-Zehnder waveguide interferometers based on the plasma dispersion effects”, Appl. Phys. Lett. 59 (7), pp 771–773 August (1991)]. In addition, the injection of free carriers has been utilized for wavelength de-multiplexing [Baojun Li et. al., “Y-Branch 1.3/1.55 μm wavelength demultiplexer based on the plasma dispersion effect”, Thin Solid Films 369 pp 419–422 (2000)]. However, no previous work on the use of the plasma dispersion effect in MOS capacitor structures for the mode control in optical wave-guides is known to the inventors.
It is therefore a purpose of the present invention to provide electro-optical devices for electrical control of the optical mode propagating in a slab wave-guide which are created monolithically on a silicon substrate.
It is another purpose of the present invention to provide electro-optical devices whose production is based entirely on well-established silicon technology.
It is yet another purpose of the present invention to provide electro-optical devices which operate at gigahertz frequencies.
It is a further purpose of the present invention to provide electro-optical devices whose cost of production is relatively low.
It is a still further purpose of the present invention to provide a method of monolithically producing electro-optical devices for electrical control of the optical mode propagating in a slab wave-guide which are created monolithically on a silicon substrate.
Further purposes and advantages of this invention will appear as the description proceeds.